Method for washing hollow fiber membrane module

Abstract

Provided is a method for washing a hollow fiber membrane module which comprises a hollow fiber membrane for filtering raw water containing a suspended component, said method comprising, in the following order, a first washing step for removing a suspended component that is accumulated on the hollow fiber membrane and a second washing step for carrying out an air scrubbing process in which gas is caused to pass through at least to the raw water side of the hollow fiber membrane, wherein, out of water that existed in the hollow fiber membrane module before washing, water in an amount corresponding to not less than 50 vol % of the capacity of the hollow fiber membrane module is removed in the first washing step.

1 . A hollow fiber membrane module comprising
 a hollow fiber membrane bundle composed of a plurality of hollow fiber membranes;   a housing in which the hollow fiber membrane bundle is housed; and   an adhesive fixing portion by which both ends of the hollow fiber membrane bundle are adhesively fixed to the housing, wherein   the hollow fiber membranes are microfiltration (MF) membranes or ultrafiltration (UF) membranes,   the adhesive fixing portion comprises
 a first adhesive fixing layer for adhesively fixing hollow fiber membranes to each other and the hollow fiber membrane bundle to an interior wall of the housing via a resin material at one end of the hollow fiber membranes; and 
 a second adhesive fixing layer for adhesively fixing the hollow fiber membranes to each other and the hollow fiber membrane bundle to an interior wall of the housing via a resin material at the other end of the hollow fiber membranes, 
   the hollow fiber membrane module comprises
 an inlet for communicating between an exterior portion of the hollow fiber membrane module and a space outside the hollow fiber membranes; 
 a filtered water port for communicating between an exterior portion of the hollow fiber membrane module and spaces inside the hollow fiber membranes; and 
 a cleaning outlet for communicating between an exterior portion of the hollow fiber membrane module and a space outside the hollow fiber membranes, and 
   all of the following conditions (A), (B), and (C) are satisfied:
 (A) a packing rate of the hollow fiber membranes, which is expressed as a ratio of a total cross-sectional area of the hollow fiber membranes to an internal cross-sectional area of the housing, is 38% or less; 
 (B) an outer diameter of the hollow fiber membranes is 1.1 mm or less; and 
 (C) a total membrane area of the hollow fiber membranes is 70 m 2  or more. 
   
     
     
         2 . The hollow fiber membrane module according to  claim 1 , wherein an effective length of the hollow fiber membranes is 1.6 m or more. 
     
     
         3 . The hollow fiber membrane module according to  claim 1 , wherein the adhesive fixing portion of the hollow fiber membrane module does not have a restricting member for restricting an arrangement of the hollow fiber membranes. 
     
     
         4 . The hollow fiber membrane module according to  claim 3 , wherein
 hollow portions of the hollow fiber membranes are open in the first adhesive fixing layer, and   hollow portions of the hollow fiber membranes are sealed at the second adhesive fixing layer.   
     
     
         5 . The hollow fiber membrane module according to  claim 1 , wherein the second adhesive fixing layer has a hole penetrating the second adhesive fixing layer. 
     
     
         6 . A filtration method, in which a filtrate is filtered using the hollow fiber membrane module according to  claim 1 , wherein
 the filtration method comprises
 filtering by external pressure filtration to cause the filtrate to pass through the hollow fiber membranes to obtain filtered water; and 
 cleaning which is carried out after the filtering, wherein 
   the cleaning is a method for cleaning a hollow fiber membrane module which comprises a hollow fiber membrane for filtering raw water containing a suspended component, comprising in the following order:   first cleaning of removing the suspended component accumulated on the hollow fiber membrane; and   second cleaning of carrying out an air scrubbing treatment by passing a gas through at least a raw water side of the hollow fiber membrane, wherein   with respect to a capacity of the hollow fiber membrane, 50% by volume or greater of water present in the hollow fiber membrane module before cleaning is removed in the first cleaning.   
     
     
         7 . The filtration method according to  claim 6 , wherein the first cleaning includes carrying out at least one treatment of the following (A1) to (A3):
 (A1) a reverse-flow cleaning treatment by passing water from a filtered water side to a raw water side of the hollow fiber membrane;   (A2) a flushing treatment by passing water through a raw water side of the hollow fiber membrane; and   (A3) a draining treatment by discharging a liquid within the hollow fiber membrane module.   
     
     
         8 . The filtration method according to  claim 6 , wherein 7% by mass or greater of a suspended component accumulated in the hollow fiber membrane is removed in the first cleaning. 
     
     
         9 . The filtration method according to  claim 6 , wherein the second cleaning includes carrying out any of the following (B1) to (B3):
 (B1) carrying out only an air scrubbing treatment by passing a gas through a raw water side of the hollow fiber membrane;   (B2) simultaneously carrying out an air scrubbing treatment by passing a gas through a raw water side of the hollow fiber membrane and a reverse-flow cleaning treatment by passing water from a filtered water side to a raw water side of the hollow fiber membrane; and   (B3) simultaneously carrying out an air scrubbing treatment by passing a gas through a raw water side of the hollow fiber membrane and a flushing treatment by passing water through a raw water side of the hollow fiber membrane.   
     
     
         10 . The filtration method according to  claim 6 , further comprising
 third cleaning of discharging the suspended component to an exterior portion of the hollow fiber membrane module after the first cleaning and the second cleaning.   
     
     
         11 . The filtration method according to  claim 10 , wherein the third cleaning includes carrying out at least one treatment of the following (C1) and (C2):
 (C1) a flushing treatment by passing water through a raw water side of the hollow fiber membrane; and   (C2) a reverse-flow cleaning treatment by passing water from a filtered water side to a raw water side of the hollow fiber membrane.   
     
     
         12 . A filtration method for filtering a filtrate using the hollow fiber membrane module according to  claim 1 , wherein
 the filtration method comprises
 filtering by external pressure filtration to cause the filtrate to pass through the hollow fiber membranes to obtain filtered water; and 
 cleaning which is carried out after the filtering, 
   the cleaning comprises in the following order:
 first cleaning of carrying out reverse-flow cleaning or flushing and a second cleaning, and 
   in the second cleaning,
 reverse-flow cleaning, in which the filtered water from an interior side to an exterior side of the hollow fiber membranes, or flushing, in which a filtrate is introduced from the inlet and discharged from the cleaning outlet; and 
 air scrubbing, in which a filtrate containing air bubbles is introduced from the inlet and discharged from the cleaning outlet and the hollow fiber membranes are shaken by the air bubbles, are carried out in combination, whereby reverse-flow cleaning-air scrubbing simultaneous cleaning or flushing-air scrubbing simultaneous cleaning is carried out to clean an exterior surface of the hollow fiber membranes. 
   
     
     
         13 . The method for cleaning a hollow fiber membrane module according to  claim 12 , further comprising third cleaning after the first cleaning and the second cleaning, wherein the third cleaning includes carrying out at least one treatment of the following (C1) and (C2):
 (C1) a flushing treatment by passing water through a raw water side of the hollow fiber membranes; and   (C2) a reverse-flow cleaning treatment by passing water from a filtered water side to a raw water side of the hollow fiber membranes.   
     
     
         14 . The filtration method according to  claim 12 , comprising
 discharging cleaning waste liquid outside the hollow fiber membranes and in hollow portions thereof from the inlet or the cleaning outlet after the cleaning.   
     
     
         15 . The filtration method according to  claim 14 , wherein the discharging includes introducing compressed air into the inlet or the cleaning outlet to forcibly discharge the cleaning waste liquid. 
     
     
         16 . The filtration method according to  claim 12 , wherein an average turbidity of the filtrate is 10 degrees or more.